Method for treating fluoroaluminosilicate glass

ABSTRACT

Fluoroaluminosilicate dental cement glasses are treated with an aqueous silanol treating solution and optionally with an additional organic compound. The treated glasses form cements with improved strength. The silanol can be ethylenically-unsaturated and can contain acidic groups, and, if so, is novel in its own right.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 07/708,467, filed May 31, 1991 now abandoned.

TECHNICAL FIELD

This invention relates to fluoroaluminosilicate glasses and to glassionomer cements.

BACKGROUND ART

In recent years, fluoroaluminosilicate ("FAS") glass cements, also knownas "glass ionomer cements", have become widely used in dentistry. Theyare fluoride-releasing and therefore cariostatic. However, they are alsorelatively fragile, as manifested by their low diametral tensilestrength ("DTS") and low fracture toughness ("K_(1c) "). Glass ionomercements are widely accepted for low stress applications such as linersand bases, but are prone to early failure in restorative applications,core build-ups and other high stress applications. This has tended tolimit clinical use of these otherwise meritorious cements.

U.S. Pat. No. 5,063,257 describes glass ionomer cements containing apolymerizable unsaturated organic compound. In several examples of the'257 patent (e.g., examples 6-8 and 14-16), the fluoroaluminosilicateglass is treated with an anhydrous alcoholic solution of anethylenically-unsaturated alkoxysilane. The resultant silane-coatedglass is dried and later mixed with a polyacrylic acid and amethacrylate monomer. The '257 patent mentions but does not exemplifytreating the glass with unsaturated carboxylic acids such as methacrylicacid, acrylic acid and maleic acid.

U.S. Pat. No. 4,250,277 describes a cement made from a treatedaluminoborate glass. The treatment involves washing the glass withammonium phosphate, in order to extend the setting time of the cement.

U.S. Pat. No. 4,376,835 describes a calcium aluminum fluorosilicateglass that has been treated with an acid. The treatment is said toreduce water sensitivity and extend setting time.

U.S. Pat. No. 4,652,593 describes a metal oxide cement containing amixture of calcium oxide and aluminum oxide. The oxide powders arecoated with a water-soluble high molecular weight substance. The coatingis said to increase crushing strength, hydrophilicity and working time,and to decrease solubility.

U.S. Pat. No. 4,808,288 describes glass ionomer cement powders made byvigorous comminution of a glass and a carboxylic acid. The powderscontain carboxylate groups.

European Published Patent Application 0 323 120 and U.S. Pat. No.4,872,936 describe photocurable cements. The '936 patent describessilane-treating an optional added filler (e.g., microfine silica) butnot a glass ionomer powder.

U.S. Pat. No. 4,673,354 describes silanol solutions that can be used toprime dental porcelains and dental alloys.

SUMMARY OF THE INVENTION

We have found that by treating the fluoroaluminosilicate glass with asilanol, substantially improved glasses can be obtained. The treatedglasses are easily mixed with aqueous polyacrylic acid solutions, haveexcellent fluoride release, and provide cements with improved DTS andimproved fracture toughness.

In our procedure, we adjust the treatment solution with an acid or baseto provide a non-neutral solution (or we employ a silane that is notonly ethylenically-unsaturated but also acid- or base-functional) and wecarry out the treatment in the presence of water. Accordingly, thesilane is converted to a silanol. The acid or base and the silanol reactwith the glass, and an improved treated glass is obtained. The treatedglass may optionally be treated with an additional organic compound ormixture of compounds to further enhance strength and fracture toughness.Thus the present invention provides, in one aspect, a method fortreating fluoroaluminosilicate glass, comprising the steps of:

a. mixing finely-divided fluoroaluminosilicate glass with an aqueoussilanol solution, optionally borne in a volatile solvent,

b. drying the glass, and optionally

c. further mixing the dried silanol treated fluoroaluminosilicate glasswith a solution of an additional organic compound or mixture of organiccompounds, optionally borne in a volatile solvent, drying the treatedglass, if necessary, to remove the volatile solvents therefrom, toprovide an essentially dry powder blend of additional organic compoundand silanol treated fluoroaluminosilicate glass or a viscous paste ofadditional organic compound and silanol treated fluoroaluminosilicateglass.

The invention also provides preferred novel treatedfluoroaluminosilicate glasses, comprising a reactiveorganoaluminosilicate particulate glass having anethylenically-unsaturated carboxylate ion-containing, siloxy-containingcoating.

In addition, the invention provides novel monomeric, oligomeric andpolymeric alkoxysilanes containing a backbone bearingethylenically-unsaturated groups and carboxylic acid groups, thebackbone being joined to the alkoxysilane via an amide group.

The treated glasses of the invention can be formulated into cementshaving outstanding physical properties and broad clinical applicability.

DETAILED DESCRIPTION

Briefly, the method of the invention involves mixing a finely-dividedfluoroaluminosilicate glass with an aqueous silanol treating solution. Awide variety of fluoroaluminosilicate glasses can be treated. Theseglasses are well known in the art, and include glasses such as thosedescribed in U.S. Pat. Nos. 3,655,605, 3,814,717, 4,043,327, 4,143,018,4,209,434 and 5,063,257. The glass preferably contains sufficientleachable fluoride to provide useful cariostatic protection when acement made from the glass is placed in the mouth. The glass preferablyis sufficiently finely divided to provide easy mixing, rapid cure andgood handling properties in dental applications. Any convenientpulverizing or comminuting means can be employed to producefinely-divided glass. Ball-milling is a convenient approach.

The starting silanes utilized to fore the silanol treating solution canbe ionic or nonionic or a combination thereof and can be monomeric,oligomeric or polymeric. Ionic silanes include anionic, cationic andzwitterionic silanes. Acidic or basic silanol treatment solutions can beprepared using ionic or nonionic silanes. Acidicethylenically-unsaturated nonionic treatment solutions are mostpreferred. Although silanols are preferred for use in the presentinvention, the hydrolysis products of titanales or zirco-aluminates can,if desired, be used in addition to or instead of silanes.

Ionic starting silanes that can be utilized to form the silanoltreatment solution include "T2909.7"N-(3-trimethoxysilylpropyl)-N-methyl-N,N-diallyl ammonium chloride,"T2921" trimethoxysilylpropylisothiouronium chloride, "T2924"N-trimethoxysilylpropyltributylammonium bromide and "T2925"N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride from PetrarchChemical Co., Inc. A particularly preferred ionic silane is "T2909.7".

Nonionic silanes useful in the practice of the invention include"A-1100" gamma-aminopropyltriethoxysilane from Union Carbide Corp. andthose listed in Column 5 lines 1-17 of U.S. Pat. No. 4,673,354. Apreferred nonionic silane is gamma-methacryloxypropyltrimethoxysilane.

The acidic or basic aqueous silanol treating solution contains amonomeric, oligomeric or polymeric silanol. The acid or base in thetreating solution can be home on the silanol, home on the silane,present as a separate component or combinations thereof. The treatingsolution is conveniently produced by dissolving a monomeric, oligomericor polymeric alkoxy silane in a volatile solvent and water. Sufficientacid or base should be added to the solution or home on the silane topromote hydrolysis of the silane to a silanol.

A preferred treatment solution is an acidic aqueous silanol treatingsolution containing a monomeric, oligomeric or polymericethylenically-unsaturated silanol. The acid in the treating solution canbe borne on the silanol, borne on the silane or present as a separatecomponent. The treating solution is conveniently produced by dissolvinga monomeric, oligomeric or polymeric ethylenically-unsaturatedalkoxysilane in a volatile solvent and water. Sufficient acid should beadded to the solution or borne on the alkoxysilane to promote hydrolysisof the alkoxysilane to a silanol.

The preferred treatment solution may optionally also contain anadditional organic compound or mixture of compounds independently havingat least one polymerizable, ethylenically unsaturated double bond and anaverage molecular weight of all species used to treat thefluoroaluminosilicate glass of up to about 5,000 units per double bond,wherein the molecular weight of each species is the weight averagemolecular weight evaluated against a polystyrene standard using gelpermeation chromatography. More preferably, the average molecular weightof all species per double bond is between about 100 and 2,500 and mostpreferably between about 250 and 1,000. A preferred amount of additionalorganic compound is up to about 50 weight %, more preferably about 5 to30 weight % and most preferably about 10 to 20 weight %, based on thetotal weight of the cement mixture. Treatment of thefluoroaluminosilicate glass with the additional organic compound ormixture of compounds may be concurrent or sequential with the silanoltreatment. Preferably, treatment of the fluoroaluminosilicate glass withthe additional organic compound follows treatment of the glass with thesilanol.

The alkoxysilane preferably contains one or more hydrolyzable alkoxygroups, one or more pendant ethylenically-unsaturated groups, andoptionally one or more pendant carboxylic acid groups. Suitablemonomeric alkoxysilanes are conveniently prepared by reacting anethylenically-unsaturated compound containing an active hydrogen groupwith an alkoxysilane containing an electrophilic group. A particularlypreferred alkoxysilane is an isocyanato-functional alkoxysilane.Suitable ethylenically-unsaturated compounds include acrylic,methacrylic, maleic, itaconic, citraconic, and aconitic acids. Othersuitable ethylenically-unsaturated compounds include2-hydroxyethylmethacrylate, 2-hydroxypropylmethacrylate, acrylamide,methacrylamide, n-allyl amine and styryl benzyl amine. Theethylenically-unsaturated compound preferably contains at least one (andpreferably two or more) carboxylic acid groups. The reaction with theisocyanato-functional alkoxysilane preferably is carried out at lessthan stoichiometric equivalence of carboxylic acid groups to isocyanatogroups, so that the resulting ethylenically-unsaturated alkoxysilanebears residual unreacted carboxylic acid groups. Suitableisocyanato-functional alkoxysilanes includeisocyanotoethyltrimethoxysilane, isocyanatopropyltrimethoxysilane, andisocyanatopropyltriethoxysilane.

Suitable polymeric alkoxysilanes are conveniently prepared by reactingan isocyanato-functional alkoxysilane of the type described above with aprecursor polymer having pendant ethylenically-unsaturated groups andactive hydrogen groups along its backbone. Preferably at least some ofthe active hydrogen groups in the precursor polymer are carboxylic acidgroups, present in sufficient stoichiometric excess so that some of thecarboxylic acid groups will remain after reaction with theisocyanato-functional alkoxysilane.

Preferred precursor polymers containing both ethylenically-unsaturatedgroups and carboxylic acid groups are described in European PublishedPatent Application No. 0 323 120. These can be reacted with anisocyanato-functional alkoxysilane to provide a particularly preferredclass of novel ethylenically-unsaturated monomeric, oligomeric andpolymeric alkoxysilanes having the formula: ##STR1## wherein R¹, R², R³and R⁴ are independently H, CH₃, COOH or CH₂ COOH; R⁵ and R⁶ areindependently divalent alkylene linking groups; each R⁷ is independentlyan alkyl group; T¹ and T² are independently terminating groups such as Hor alkyl; w is 0 to 12; and each of x, y and z is at least one.Preferably R⁵ is C₂ H₄, R⁶ is C₃ H₆, R⁷ is CH₃ or C₂ H₅, T¹ and T² are Hor CH₃, and w is 0 to 6.

Suitable additional organic compounds for treating the glass or fillerinclude monomers, oligomers or polymers. If the additional organiccompound is a monomer then the monomer may be monofunctional (i.e.,containing only one ethylenically unsaturated double bond) ormultifunctional (i.e., containing two or more double bonds). Presentlypreferred monomers are multifunctional with the presently most preferredmonomers containing two double bonds.

If the additional organic compound is a polymer then the polymer may bea linear, branched or cyclic polymer of ethylenically unsaturatedmonomers or it can be polymeric compound like polyester, polyamide,polyether, polyethyleneglycol, polysaccharide, cellulosic,polyproplylene, polyacrylonitsile, polyurethane, poly(vinyl chloride),poly(methyl methacrylate), phenol-formaldehyde, melamine-formaldehyde,and urea-formaldehyde.

Presently preferred additional organic compounds contain bothethylenically-unsaturated groups (e.g., acrylate, methacrylate, alkeneor acrylamide groups which are capable of further hardening reaction,i.e., crosslinking or copolymerizing with themselves or other componentsof the cement mixture) and hydrophilic groups (e.g., ethyleneoxy groups,alcohol groups and esters). Hydrophilic groups on the additional organiccompounds may aid in dispersing the organic compound in the treatmentsolution when applying the treatment to the glass, and also may aid inthe dispersability of the glass in the cement-forming liquid. It will beunderstood that these benefits may be present in mixtures of additionalorganic compounds when one compound has no or few hydrophilic groups andanother compound has many hydrophilic groups. Preferred additionalorganic compounds contain ethyleneglycol groups.

Examples of suitable additional organic compounds include mono-, di- orpolyfunctional acrylates and methacrylates such as methyl acrylate,methyl methacrylate, ethyl acrylate, isopropyl methacrylate, n-hexylacrylate, styryl acrylate, allyl acrylate, glycerol diacrylate, glyceroltriacrylate, ethyleneglycol diacrylate, diethyleneglycol diacrylate,triethyleneglycol dimethacrylate ("TEGDMA"), tetraethyleneglycoldimethacrylate, polyethyleneglycol dimethacrylate (e.g., "PEG₂₀₀ DMA","PEG₄₀₀ DMA" and "PEG₆₀₀ DMA" with an average of 4.5, 9 and 13.6ethyleneglycol groups or "units" respectively), 1,3-propanedioldiacrylate, 1,3-propanediol dimethacrylate, trimethylolpropanetriacrylate, 1,2,3-butanetriol trimethacrylate, 1,4-cyclohexanedioldiacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, sorbitol hexacrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,tris-hydroxyethylisocyanurate triacrylate, beta-methacrylaminoethylmethacrylate,2,2-bis[4-(2-hydroxy-3-methacryloyloxy-propoxy)phenyl]propane("BIS-GMA"), 2,2-bis[4-(2-methacryloyloxyethoxy)-phenyl]propane,2,2-bis[4-methacryloyloxyphenyl]propane, "SARTOMER" 350 ("SR350",Sartomer Corp.) and mixtures thereof. Other suitable monomers includeunsaturated amides such as 2-acrylamidoglycolic acid, methylenebis-acrylamide, methylene bis-methacrylamide, 1,6-hexamethylenebis-acrylamide, tetra acrylamido glycuril (" TAGU") anddiethylenetriamine tris-acrylamide. Suitable oligomeric or polymericresins include up to 5000 molecular weight polyalkylene glycols,acrylated or methacrylated oligomers such as those of U.S. Pat. No.4,642,126, acrylated urethanes such as "SARTOMER" 9503, 9504 and 9505(Sartomer Corp.), "INTEREZ" CMD 8803, 8804 and 8805 (RadcureSpecialties, Inc.), and "PHOTOMER 6060, 6110 and 6160 (Henkel Corp.), aswell as acrylated polyester oligomers such as "EBERCRYL" 830 (RadcureSpecialties, Inc.). Mixtures of free-radically polymerizable monomers,oligomers or polymers can be used if desired.

Examples of presently preferred additional organic compounds includemono-, di- or polyfunctional acrylates and methacrylates such asethyleneglycol diacrylate, diethyleneglycol diacrylate,triethyleneglycol dimethacrylate, tetraethyleneglycol dimethacrylate,polyethyleneglycol dimethacrylate (e.g., "PEG₂₀₀ DMA", "PEG₄₀₀ DMA" and"PEG₆₀₀ DMA" with an average of 4.5, 9 and 13.6 ethyleneglycol groups or"units" respectively), BIS-GMA, "SARTOMER" 350 and mixtures thereof.Other presently preferred monomers include unsaturated amides such astetra acrylamido glycuril. Presently preferred oligomeric or polymericresins include up to 5000 molecular weight polyalkylene glycols.

Presently most preferred additional organic compounds includetriethyleneglycol dimethacrylate, tetraethyleneglycol dimethacrylate,"PEG₂₀₀ DMA", BIS-GMA, "SARTOMER" 350, tetra acrylamido glycuril andmixtures thereof.

As mentioned above, the silanol treating solution contains themonomeric, oligomeric or polymeric silanol, water and an optionalvolatile solvent. The silanol should be present in the treating solutionin an amount sufficient to increase by more then the experimental errorof measurement the DTS of a glass ionomer cement made from a reactivepowder treated with the solution. A preferred aamount of silanol in thetreating solution is from about 0.1 to about 20 weight %, morepreferably about 0.5 to about 10 weight %, based on the total weight ofthe treating solution.

The water in the treating solution facilitates hydrolysis of the silane.In order to discourage premature solution condensation of the silanol,the water preferably is substantially free of fluoride and othercontaminants. Deionized water is preferred. Preferred aamounts of waterare about 20 to about 99.9%, more preferably about 30 to about 95%,based on the total weight of the treating solution.

The acid or base in the treating solution should be capable of promotinghydrolysis of the silane to a silanol. Preferably the acid or base isborne on the silane. If present as a separate ingredient, the acid orbase can be water-soluble and organic or inorganic. Preferred acidsinclude formic acid, acetic acid, trifluoroacetic acid, propionic acid,pentafluoropropionic acid, hydrochloric acid, nitric acid, sulfuricacid, phosphoric acid, lactic acid, citric acid, and tartaric acid.Acetic acid is a particularly preferred separate acid. Preferred basesinclude sodium hydroxide, ammonium hydroxide, potassium hydroxide,barium hydroxide, lithium hydroxide, magnesium hydroxide, calciumhydroxide, sodium bicarbonate, ammonia, methylamine, dimethylamine,trimethylamine, ethylamine, diethylamine, n-propylamine, n-butylarnine,isobutylamine, sec-butylamine, and tert-butylamine. Sodium hydroxide isa particularly preferred separate base. Quaternary ammonium salts thathydrolyze to provide an acidic or basic solution can also be used. Suchquaternary ammonium salts include ammonium bromide, ammonium chloride,isothiouronium bromide and isothiouronium chloride.

The amount of acid or base should, as noted above, be sufficient topromote hydrolysis of the silane. The desired aamount of acid or basecan conveniently be monitored by measuring the pH of the treatingsolution. A preferred acidic pH is 5 or less, more preferably about 1 toabout 4.5, and most preferably about 3 to about 4. A preferred basic pHis 8 or higher, more preferably about 9 to about 12, and most preferablyabout 9 to 11.

The optional volatile solvent in the treating solution serves todissolve the silane and to aid in formation of a thin film of thetreating solution on the finely-divided glass. Alcohol and ketonesolvents are preferred. Methanol, ethanol, propanol, isopropanol,tert-butanol and acetone are particularly preferred solvents. Mostpreferably, the solvent is an alcohol, such as the alcohol formed byhydrolysis of, for example, an alkoxysilane. Methanol is thus apreferred solvent for methoxysilanes, and ethanol is a preferred solventfor ethoxysilanes.

When used, the aamount of solvent should be at least sufficient todissolve the silane and form a homogeneous single-phase solution. Apreferred aamount of solvent is about 40 weight % or more, with amountsbetween about 40 and 60 weight % being most preferred.

The solvent can be omitted by carrying out hydrolysis of the silaneusing vigorous stirring and continuous addition of the ingredients. Thesilane generally has poor water solubility, but the silanol has goodwater solubility and preferentially will be extracted into the water.

The ingredients in the treating solution are prepared by mixing them inany convenient order. Ordinarily, the water (and acid or base if presentas a separate ingredient) are combined with the solvent and the silane.The resulting mixture is stirred for a time sufficient to promotehydrolysis of the silane, and then preferably used before the onset ofhaziness (which indicates undesirable condensation of the silanol).

The finely-divided glass and treatment solution, optionally containingadditional organic compound, are combined by slurrying or otherconvenient mixing techniques. Mixing times of at least 30 minutes ormore are preferred, and mixing times of about 1 to about 2 hours areparticularly preferred.

The treated glass can be dried using any convenient technique. Thenecessary drying temperature and time will depend in part upon thevolatility of the solvent, the surface area of the glass and the mannerin which drying is carried out. Drying times can be verified throughstandard weight loss measurements. Oven drying in a forced air oven isrecommended, with overnight drying temperatures of about 30° to 100° C.being preferred.

If desired, the dried silanol-treated fluoroaluminosilicate glass may befurther blended with a solution of additional organic compound using anysuitable technique (e.g., batch mixing using a double planetary mixer ora twin shell powder mixer). The additional organic compound is presentlypreferably blended with the dry glass without the addition of solvents,as this avoids the necessity of a second drying step. Solvents may beutilized, however, to facilitate an even distribution of additionaltreatment. Such solvents can be removed using standard techniques aspreviously mentioned. Care should be taken to avoid harsh conditionsduring the drying steps (e.g., excessively high temperatures orprolonged exposure to an oxygen free atmosphere) which might degrade theethylenically unsaturated double bond of the treatment material.

Following treatment, the glass preferably is screened or lightlycomminuted in order to break up agglomerates. The treated glass can bestored as is or, if desired, combined with other adjuvants such aspigments, nonvitreous fillers, inhibitors, accelerators and otheringredients that will be apparent to those skilled in the art.

The treated glass can be made into a cement by combining it in thepresence of water with any of the polyacids used in conventional glassionomer cements. Suitable polyacids include acidic liquids such as thosedescribed in U.S. Pat. Nos. 3,814,717 and 4,016,124, and light-cureliquids such as those described in U.S. Pat. Nos. 4,872,936 and5,063,257 and European Published Pat. Application Nos. 0 323 120 and 0329 268.

The treated glass preferably retains the ability to release clinicallyuseful aamounts of fluoride ion when made into a cured cement by mixingwith an appropriate polyalkenoic acid (e.g., aqueous polyacrylic acid).Fluoride release can conveniently be measured using the procedure setout in EXAMPLE 19 of European Published Pat. Application No. 0 323 120.When so measured, the silanol treated glass preferably has a greaterfluoride release than a comparison glass treated with a silane treatmentsolution.

In order to provide light cure capability, glass ionomer cements madefrom the treated glass preferably include a free radical initiator,e.g., a photoinitiator. Suitable photoinitiators are described inEuropean Published Pat. Application No. 0 323 120. The cement cancontain adjuvants such as viscosity modifiers, ethylenically-unsaturatedresins, suffactants, and other ingredients that will be apparent tothose skilled in the art.

Glass ionomer cements made from treated glasses of the invention aremixed and clinically applied using conventional techniques. However, thecements will have particular utility in clinical applications whereconventional glass ionomer cements typically have been deficient. Suchareas include high-stress applications such as restoratives (e.g.,posterior tooth restoration, incisal edge replication and bulk dentinreplacement), and crown core build-ups.

The invention is further described in the following illustrativeexamples, which should not be construed as limiting the scope of theinvention. Unless otherwise indicated, all parts and percentages are ona weight basis.

PREPARATORY EXAMPLE 1 Monomeric Ethylenically-Unsaturated AcidicAlkoxysilane

A solution of 13 parts itaconic acid in 88.6 parts dry tetrahydrofuran(THF) was placed in a glass reaction vessel equipped with a refluxcondenser, drying tube, addition port and stirrer. Next, 0.1 partsdibutyltin dilaurate (DBTDL) and 0.06 pans butylated hydroxytoluene(BHT) were added to the reaction vessel. The temperature was raised to45° C. Over a 65 minute period, 24.7 pans3-isocyanatopropyltriethoxysilane (IPTES) were added dropwise to thereaction mixture. The reaction mixture was stirred for 16 hours at 45°C. Examination by infrared spectroscopy (IR) showed that the isocyanatopeak at 2250 cm⁻¹ had virtually disappeared. THF was removed by rotaryevaporation using an air bleed. A small amount of solid separated outand was removed by filtration. The filtrate was analyzed by IR anddetermined to be a mixture of the following isomers:

    H.sub.2 C═C(COOH)CH.sub.2 C(O)NH(CH.sub.2).sub.3 Si(OC.sub.2 H.sub.5).sub.3 and

    H.sub.2 C═C(CH.sub.2 COOH)C(O)NH(CH.sub.2).sub.3 Si(OC.sub.2 H.sub.5).sub.3

IR data: COOH, 1729 cm⁻¹ ; C═C(C))H, 1602 cm⁻¹ ; C═CCH₂ COOH, 1630 cm⁻¹; SiOC₂ H₅, 972 and 1114 cm⁻¹ ; and C(O)NH, 1582 cm⁻¹.

PREPARATORY EXAMPLE 2

Ethylenically-Unsaturated Acidic Copolymer

A glass reaction vessel like that used in PREPARATORY EXAMPLE 1 (buthaving two addition pore) was charged with 132.9 parts THF. One additionport was charged with an acid solution containing 58.6 parts acrylicacid and 26.0 parts itaconic acid in 150.6 parts THF. The other additionport was charged with an initiator solution containing 0.82 partsazobisisobutyronitrile (AIBN) in 115 parts THF. The reaction vessel wasflushed with nitrogen and hated to about 60° C. with mechanical sting.The acid solution was added at a rate of about 9 pans every 15 minutesand the initiator solution was added at a rate of about 4.5 parts every15 minutes. The temperature of the reaction vessel was kept at about62°-64° C. After addition of the acid and initiator solutions wascomplete, the reaction mixture was stirred at about 64° C. for 17 hours.IR analysis showed that the ethylenically-unsaturated groups of thestarting acids had virtually disappeared, and that the polymerizationreaction was complete.

The reaction mixture was allowed to cool to about 35° C. A mixture of0.15 parts BHT, 0.15 parts triphenylstibene (TPS) and 1.03 parts DBTDLwas added to the reaction vessel. A stream of air was introduced intothe reaction mixture and the temperature was increased to about 40° C. Asolution of 35.34 parts 2-isocyanatoethyl methacrylate (IEM) in 22 partsTHF was added dropwise over a period of about 1.5 hours. The reactionmixture was stirred at about 40° C. for an additional hour, followed bystirring at about 20° C. for 18 hours. The reaction mixture wasconcentrated under vacuum to a syrupy consistency. It was thenprecipitated into five times its volume of ethyl acetate. The resultingprecipitate was filtered, washed with ethyl acetate and dried undervacuum with an air bleed. The polymer yield was 98%, based on thestarting amounts of acrylic acid, itaconic acid and IEM. About 10% ofthe carboxylic acid groups of the polymer reacted with the IEM. Theresulting ethylenically-unsaturated acidic copolymer had the followingstructure: ##STR2## where R and R' are independently H, COOH or CH₂COOH.

PREPARATORY EXAMPLES 3-5 Polymeric Ethylenically-Unsaturated AcidicAlkoxysilanes

The copolymer of PREPARATORY EXAMPLE 2 was reacted with anisocyanate-functional alkoxysilane by dissolving 10.59 parts of thecopolymer in 44.3 parts dry THF. Next, solutions of varying amounts ofIPTES and 0.02 parts DBTDL in 4.43 parts THF were added to the reactionvessel. Each reaction mixture was stirred for 18 hours at 40° C. IRanalysis showed the virtual disappearance of the isocyanato peak. Thedesired products were precipitated in 226 parts ethyl acetate, filteredand dried under vacuum. The nominal compositions of the resultingpolymeric ethylenically-unsaturated acidic silanes are set out below inTable I.

                  TABLE I                                                         ______________________________________                                        Preparatory                                                                             IPTES,    mole % in copolymer                                       Example   Parts     COOH     Si(OC.sub.2 H.sub.5).sub.3                                                             C═C                                 ______________________________________                                        3         1.31      81.8     4.2      16                                      4         2.47      75.6     8.4      16                                      5         3.75      71.4     12.6     16                                      ______________________________________                                    

IR data: COOH, 1730 cm⁻¹ ; C═C, 1620 cm⁻¹ ; SiOC₂ H₅, 960 and 1120 cm⁻¹and C(O)NH, 1530 cm⁻¹.

PREPARATORY EXAMPLES 6-8 Untreated Fluoroaluminosilicate Glasses

The ingredients set out below in Table II were mixed, melted in an arcfurnace at about 1350°-1450° C., poured from the furnace in a thinstream and quenched using chilled rollers to provide amorphoussingle-phase fluoroaluminosilicate glasses.

                  TABLE II                                                        ______________________________________                                                 Preparatory Preparatory Preparatory                                  Ingredient                                                                             Ex. 6, parts                                                                              Ex. 7, parts                                                                              Ex. 8, parts                                 ______________________________________                                        SiO.sub.2                                                                              37          37          37                                           AlF.sub.3                                                                              23          23          23                                           SrO      20          0           20                                           CaF.sub.2                                                                              0           20          0                                            Al.sub.2 O.sub.3                                                                       10          10          10                                           AlPO.sub.4                                                                             7           0           0                                            Na.sub.3 AlF.sub.6                                                                     6           6           6                                            P.sub.2 O.sub.5                                                                        4           0           4                                            ______________________________________                                    

The glasses of PREPARATORY EXAMPLES 6, 7 and 8 were ball-milled toprovide pulverized frits with surface areas of 2.6, 3.3 and 2.7 m² /grespectively, measured using the Brunauer, Emmet and Teller (BET)method.

PREPARATORY EXAMPLE 9 Treated Nonreactive Filler

25.5 Parts silica sol ("LUDOX" LS, E.I. duPont de Nemours & Co.) wereacidified by the rapid addition of 0.255 parts concentrated nitric acid.In a separate vessel, 12.9 parts ion-exchanged zirconyl acetate(Magnesium Elektron Inc.) were diluted with 20 parts deionized water andthe resultant solution acidified with 0.255 parts concentrated nitricacid. The silica sol was pumped into the stirred zirconyl acetatesolution and mixed for one hour while filtering the stirred mixturethrough "CUNO" 5 micrometer and 1 micrometer filters (CommercialIntertech Corp.). The stirred, filtered mixture was further falteredthrough a 1 micrometer "HYTREX" falter (Osmonics, Inc.) followed by a0.22 micrometer "BALSTON" falter (Balston Inc.). The filtrate was pouredinto trays to a depth of about 25 mm and dried at 65° C. in a forced airoven for about 24 hours. The resulting dried material was removed fromthe oven and tumbled through a rotary tube furnace (Harper FurnaceCorporation) preheated to 600° C. 21 Parts of calcined microparticleswere obtained. The calcined microparticles were comminuted in a tumblingball mill until all of the microparticles were less than 10 micrometersin particle diameter. 0.3 Part portions of the milled microparticleswere placed in ceramic saggers and fired in an electric kiln (HarperFurnace Corporation) in air at 825° C. for 1 hour. The firedmicroparticles were allowed to cool in air. The cooled microparticleswere slurried in hydrolyzed gamma-methacryloxypropyl trimethoxysilane("A-174", Union Carbide Corp.), dried in a forced air oven and screenedthrough a 74 micrometer screen. The treated filler particles contained11.1% silane.

COMPARATIVE EXAMPLE 1

Using the general procedure outlined in Examples 6 and 7 of the '257patent (with some minor variations not believed to affect the result), asilane-treated glass, cement solution and cement were prepared asfollows:

Using a yellow safelight, the glass of PREPARATORY EXAMPLE 6 wasscreened through a 74 micron mesh sieve. 100 Parts of the glass powderswere mixed in a beaker with 20 pans of a 10% solution of A-174 inethanol to treat the glass with the silane. The mixture was heated at110° C. for 2 hours over a steam dryer. 100 Parts of the silane-treatedpowders were mixed in a mortar with 1 part dimethylaminoethylmethacrylate (DMAEM).

30 Parts of a 4:1 acrylic acid:itaconic acid copolymer having an averagemolecular weight (M_(w)) of about 17,500 (measured using gel permeationchromatography (GPC) with THF as the GPC solvent, and evaluated againsta polystyrene standard), were combined with 30 parts2,2'-bis[3-(4-phenoxy)-2-hydroxypropane-1-methacrylate]propane, 10 partsdi-2-methacryloxy-ethyltetramethylene dicarbamate, 30 parts distilledwater, 1.5 parts polyoxyethylene sorbitan monooleate ester and 0.5 partspolyoxyethylene sorbitan monostearate ester. The ingredients were mixedfor 4.5 hours using a paint shaker. The resulting aqueous cementsolution was cloudy and thus not completely homogenous. 0.25 Partscamphorquinone (CPQ) and 0.05 parts BHT were added to the solution.

The silane-treated powder and the cement solution were mixed for 1minute using a 2.6:1 powder:liquid (P:L) ratio. The resulting cement waspacked into a 4 mm inside diameter glass tube, capped with siliconerubber plugs, and axially compressed at about 0.28 MPa. About 1.5minutes after the start of mixing, the sample was exposed for 80 secondsto light from two oppositely-disposed visible light curing lamps("VISILUX2" curing lamp, 3M). Five cured samples were evaluated todetermine the avenge compressive strength (CS) and DTS, using themeasurement methods described in EXAMPLE 14 of European Published Pat.Application No. 0 323 120. An average CS of 130 MPa and an average DTSof 14.3 MPa were obtained. The cement was evaluated for fluoride releaseusing the measurement method set out in EXAMPLE 19 of European PublishedPat. Application No. 0 323 120. The results for the fluoride releasemeasurement are set out below in EXAMPLE 1.

EXAMPLE 1

The procedure of COMPARATIVE EXAMPLE 1 was repeated, but the glasspowder was treated using the method of the present invention. 100 Partsof the untreated glass powder of PREPARATORY EXAMPLE 6 were mixed withan aqueous, acidic silanol solution prepared by combining 2.08 partsA-174 silane, 25.3 parts methanol and 24 parts water, acidifying thesolution to pH 3.5 using trifluoroacetic acid (TFA) and stirring for onehour. IR analysis established the presence of a peak at about 3510 cm⁻¹,indicative of the presence of a silanol group. This peak was not presentin the silane treating solution of COMPARATIVE EXAMPLE 1.

The glass powder and silanol solution were stirred together for 4.25hours, then dried overnight in a 45° C. oven. The treated glass powderwas sieved through a 74 micron mesh screen. Analysis by DRIFTestablished the presence of peaks centered at about 1550 to 1610 cm⁻¹,indicative of the presence of carboxylate ions. These peaks were notpresent in the treated glass of COMPARATIVE EXAMPLE 1.

When mixed at a 2.6:1 P:L ratio and evaluated using the method ofCOMPARATIVE EXAMPLE 1, cements with an average CS of 152 MPa and anaverage DTS of 29 MPa were obtained. Although the only difference inprocedure for this example (vs. COMPARATIVE EXAMPLE 1) was the use of anaqueous acidic silanol treating solution (rather than an anhydrousalkoxysilane treating solution), the observed DTS was two times higherthan mat of COMPARATIVE EXAMPLE 1.

The cement of the invention was evaluated for fluoride release andcompared to the cement of COMPARATIVE EXAMPLE 1. The results were asfollows:

                  TABLE III                                                       ______________________________________                                                 Cumulative                                                                    fluoride release,                                                             μg/g                                                                         COMPARATIVE                                                        Days       EXAMPLE 1     EXAMPLE 1                                            ______________________________________                                         0         3.0           13.2                                                 12         51.8          362.0                                                32         59.7          726.0                                                41         69.4          756.1                                                84         170.4         1100.4                                               ______________________________________                                    

The cement of the invention exhibited much greater fluoride release thanthe comparison cement.

EXAMPLES 2-16

For EXAMPLES 2-5, the procedure of EXAMPLE 1 was repeated using theglass of PREPARATORY EXAMPLE 6. The treatment solutions employed "A-174"silane, methanol, water and TFA. Cement test samples were formed bycombining the treated glasses at a 1.4:1 P:L ratio with Liquid A inTable IV.

The treatment solution of EXAMPLE 6 was prepared by mixing A-174 silaneand water, adjusting the pH of the solution to 3.01 with acetic acid andstirring for one-half hour. The glass of PREPARATORY EXAMPLE 8, but witha surface area of 2.8 m² /g instead of 2.7 m² /g, was mixed with thetreating solution. An additional 15 pans water was added and the glasspowder and silanol solution were stirred for 1.5 hours. The treatedglass was dried overnight in a 45° C. oven and then sieved through a 74micron mesh screen. Cement test samples were formed by combining thetreated glass at a 2.2:1 P:L ratio with Liquid B in Table IV.

The treatment solution of EXAMPLE 7 was prepared by mixing A-174 silaneand water, adjusting the pH of the solution to 10.03 with a 10% sodiumhydroxide solution and stirring for one hour. The glass of PREPARATORYEXAMPLE 8 was mixed with the treating solution, dried at 30° C. for 2.5days and ground to a fine powder using a mortar and pestle. Cement testsamples were formed by combining the treated glasses at a 2.2:1 P:Lratio with Liquid B in Table IV.

The treatment solutions of EXAMPLES 8-11 were prepared by mixing theionic silanes listed in Table V in water and adjusting the pH of thesolution with TFA and stirring for one hour. The glass of PREPARATORYEXAMPLE 8 was independently mixed with each treating solution, dried at30° C. for 2.5 days and ground to a fine powder using a mortar andpestle. Cement test samples were formed by combining each of the treatedglasses at a 2.2:1 P:L milo with Liquid B in Table IV.

The treatment solution of EXAMPLE 12 employed the acidic monomericsilane of PREPARATORY EXAMPLE 1, ethanol and water. No other acidaddition was required. The glass of PREPARATORY EXAMPLE 6 was mixed withthe treating solution and dried as described for EXAMPLE 1. Cement testsamples were formed by combining the treated glasses at a 1.4:1 P:Lratio with Liquid A in Table IV.

The treatment solutions of EXAMPLES 13-16 employed the acidic polymericsilane of PREPARATORY EXAMPLE 3, ethanol and water. No other acidaddition was required. The glass of PREPARATORY EXAMPLE 6 wasindependently mixed with each treating solution and dried as describedfor EXAMPLE 1. Cement test samples were formed by combining the treatedglasses at a 1.4:1 P:L ratio with Liquid A in Table IV.

A cement composition ("Control A") made from untreated glass wasprepared and evaluated as a control. A further control composition("Control B") was prepared by treating 100 pans glass with a treatmentsolution containing 4 parts of the dry copolymer of PREPARATORY EXAMPLE5 (viz., a copolymer without alkoxysilane groups), 25.1 parts ethanoland 80 parts water. A final control composition ("Control C") wasprepared by treating the glass with a treatment solution containing 4parts of a 4:1 acrylic acid:itaconic acid copolymer (made by extractingand drying a portion of the reaction mixture of PREPARATORY EXAMPLE 2before the BHT, TPS, DBTDL and IEM were added), 25.1 pans ethanol and 80parts water.

Cement test samples were prepared by combining the treated glasses witha cement-forming copolymer solution made by mixing the ingredients setout below in Table IV.

                  TABLE IV                                                        ______________________________________                                                               Liquid A,                                                                              Liquid B,                                     Ingredients            Parts    Parts                                         ______________________________________                                        Dry copolymer of PREP. EXAMPLE 2                                                                     50       50                                            Water                  30       30                                            2-Hydroxyethyl methacrylate                                                                          20       20                                            Diphenyliodonium chloride                                                                            2.5      0                                             Diphenyliodonium hexafluorophosphate                                                                 0        1.0                                           CPQ                    0.5      0.25                                          BHT                    0        0.05                                          ______________________________________                                    

Set out below in Table V are the example number, the type of silane, thesilane:alcohol:water:glass ratio, the pH of the silanol treatmentsolution, the weight percent silanol on the glass (based on the weightof the starting materials, without accounting for the lost weight ofalkoxy groups in the hydrolyzed silane or the lost weight of waterproduced by condensation of the silanol on the glass surface), and theCS and DTS for the final cements.

                  TABLE V                                                         ______________________________________                                                       Silane:alcohol:                                                Ex.            water:glass      Wt %  CS,  DTS,                               No.   Silane   ratio       pH   silanol                                                                             MPa  MPa                                ______________________________________                                        2     A-174    0.6:18.8:16:100                                                                           3.5  0.6   156  29                                 3     A-174    2:25.2:24:100                                                                             3.5  2     172  31                                 4     A-174    4:25:25:100 3.45 4     207  31                                 5     A-174    8:41.2:12:100                                                                             3.1  8     168  33                                 6     A-174    4:0:40:100  3.01 4     223  34                                 7     A-174    3.8:0:100:100                                                                             10.03                                                                              3.8   134  17                                 8     T2909.7  4.6:4.6:100:100                                                                           3.05 4.6   136  24                                 9     T2921    4.6:0:100:100                                                                             3.05 4.1   125  17                                 10    T2924    8.1:8.1:100:100                                                                           3.05 8.1   132  16                                 11    T2925    3.6:3.6:100:100                                                                           3.05 3.6   119  16                                 12    P.E.1.sup.1                                                                            4:25.1:80:100                                                                             3.2  4     140  31                                 13    P.E.3.sup.2                                                                            2:25.1:80:100                                                                             3.1  2     152  30                                 14    P.E.3    4:25.1:80:100                                                                             3.2  4     154  31                                 15    P.E.3    4:25.6:48:100                                                                             3.35 4     176  26                                 16    P.E.3    8:25.1:80:100                                                                             3.2  8     147  24                                 Ct. A None     N.A..sup.3  N.A. 0     143  15                                 Ct. B.sup.4                                                                         None     0:25.1:80:100                                                                             2.9  0     142  14                                 Ct. C.sup.5                                                                         None     0:25.1:80:100                                                                             1.6  0     136  18                                 ______________________________________                                         .sup.1 "P.E.1" = Monomeric silane of PREPARATORY EXAMPLE 1.                   .sup.2 "P.E.3" = Polymeric silane of PREPARATORY EXAMPLE 3.                   .sup.3 Not applicable (no treatment).                                         .sup.4 Treated with a treatment solution containing 4 parts of the            silanefree dry copolymer of PREPARATORY EXAMPLE 5 per 100 parts of glass.     .sup.5 Treated with a treatment solution containing a 4:1 acrylic             acid:itaconic acid copolymer that did not contain ethylenic unsaturation      or alkoxysilane groups.                                                  

The data shown above illustrate the significant increases in DTSprovided by the invention. For example, the Control A cement had a DTSof 15 MPa, while in many cases the cements of the invention had DTSvalues that were 1.6 to 2.2 times higher (24 to 33 MPa). The cements ofthe invention would therefore be much better suited to high stressapplications.

The cements of the invention also had higher DTS values than thoseobtained for the Control B and Control C cements. This demonstrated thatthe improved DTS values were not due merely to the use of treatingsolutions containing ethylenically-unsaturated copolymers or acidiccopolymers.

The cements of EXAMPLES 7-11 and Control A were evaluated for fluoriderelease on day 0 and after 12 days using the measurement method set outin EXAMPLE 19 of European Published Pat. Application No. 0 323 120 andcompared to the cement of COMPARATIVE EXAMPLE 1. The results areprovided in Table VI.

                  TABLE VI                                                        ______________________________________                                                         Cumulative fluoride                                                           release, μg/g                                             EXAMPLE            Day 0    Day 12                                            ______________________________________                                        COMPARATIVE EX. 1  3.0      51.8                                              Control A          19.0     350.0                                             7                  8.1      214.7                                             8                  27.9     259.9                                             9                  13.9     211.4                                             10                 19.6     359.6                                             11                 21.3     285.4                                             ______________________________________                                    

The cements of the invention exhibited much greater fluoride releasethan the comparison cement.

EXAMPLE 17

The procedure of EXAMPLE 14 was repeated using a glass with a 3.6 m² /gsurface area. The treated glass was mixed with a copolymer solution likethat of Liquid A in Table IV, but made from a different copolymer. Thecopolymer was made like the copolymer of PREPARATORY EXAMPLE 5, butusing a 2:3 molar ratio of acrylic acid:itaconic acid (which formed acopolymer having a M_(w) of 9,450 by GPC), and reacting 34% of thecopolymer's carboxylic acid groups with IEM. Cements made using theresulting copolymer solution at a 1.4:1 P:L ratio had a CS of 170 MPaand a DTS of 31 MPa.

EXAMPLES 18-22

The procedure of EXAMPLES 2-5 was repeated, using the glass ofPREPARATORY EXAMPLE 7. Different treating solutions were employed, alongwith an untreated control.

The treatment solutions of EXAMPLES 18, 19 and 20 employed the polymericnonionic alkoxysilane of PREPARATORY EXAMPLE 3, methanol and water. Noother acid addition was required. The treatment solution of EXAMPLE 21employed the polymeric nonionic alkoxysilane of PREPARATORY EXAMPLE 4,ethanol and water. Again, no other acid addition was required. Thetreatment solution of EXAMPLE 22employed the polymeric nonionicalkoxysilane of PREPARATORY EXAMPLE 3, ethanol and water. Again, noother acid addition was required. The control composition ("Control D")contained untreated glass. The cement-forming copolymer solution wasLiquid A in Table IV.

Set out below in Table VII are the example number, the type of silane,the silane:alcohol:water:glass ratio, the pH of the silanol treatmentsolution, the weight percent silanol on the glass, and the CS and DTSfor the final cements.

                  TABLE VII                                                       ______________________________________                                        Ex.           Silane:alcohol:   Wt %  CS,  DTS,                               No.   Silane  water:glass ratio                                                                          pH   silanol                                                                             MPa  MPa                                ______________________________________                                        18    P.E.3.sup.1                                                                           2:25.1:100:100                                                                             4.2  2     156  28                                 19    P.E.3   4:25.1:100:100                                                                             3.2  4     172  34                                 20    P.E.4.sup.2                                                                           4:50.2:16:100                                                                              3.2  4     164  31                                 21    P.E.3   6:25.1:100:100                                                                             3.2  6     173  31                                 22    P.E.3   12:50.2:80:100                                                                             3.4  12    132  23                                 Con-  None    N.A          N/A  0     164  21                                 trol D                                                                        ______________________________________                                         .sup.1 "P.E.3" = Polymeric nonionic alkoxysilane of PREPARATORY EXAMPLE 3     .sup.2 "P.E.4" = Polymeric nonionic alkoxysilane of PREPARATORY EXAMPLE 4                                                                              

The data shown above further illustrate the significant DTS improvementprovided by the invention. Cements made from a glass treated using themethod of the invention had higher DTS values than the Control D cement.

EXAMPLE 23

The ingredients set out below in Table VIII were mixed together andstirred magnetically for 30 minutes at ambient temperature.

                  TABLE VIII                                                      ______________________________________                                               Ingredient                                                                             Parts                                                         ______________________________________                                               A-174 silane                                                                           2.0                                                                  methanol 12.6                                                                 water    12.5                                                                 acetic acid                                                                            0.22                                                          ______________________________________                                    

The mixture was added to 50.02 parts of a glass powder like that ofPREPARATORY EXAMPLE 6 (but having a surface area of 2.8 m² /g) andslurried for 1.5 hours at ambient temperature. The slurry was thenpoured into a plastic-lined tray and dried for 20 hours at 45° C. Thedried powder was sieved through a 74 micron mesh screen.

A DRIFT spectrum of the treated powder showed absorbance peaks at 2953,2932, 2892, 1719, 1696, 1636, 1580, 1452 and 1400 cm⁻¹. The last threepeaks indicate the presence of carboxylate ions.

A cement mixture was formed by spatulating 2.2 parts of the treatedpowder with 1.0 part of a liquid like Liquid A in Table IV (but with 1.0part diphenyliodonium hexafluorophosphate rather than 2.5 partsdiphenyliodonium chloride). The cement had a CS of 210 MPa and a DTS of30 MPa. The cement had an excellent balance of physical properties andaesthetics.

EXAMPLE 24 Modification of a Commercial Fluoroaluminosilicate Glass

In a series of four runs, "VITREBOND" Glass Ionomer Liner/Base (3M)glass powder (surface area of 2.2-2.5 m² /g) was independently treatedwith varying concentrations of a silanol treatment solution. The silanoltreatment solutions were prepared by independently adding 0.0072 parts,0.036 parts, 0.054 parts and 0.259 parts A-1100 silane to 12 partsdeionized water to form treatment solutions of 0.1%, 0.5 %, 1.0% and5.0% silanol respectively. The pH of the solutions was 10.8. No baseaddition was required. After stirring for 30 minutes, 5 parts VITREBONDglass powder was added to each solution. Each treated glass was allowedto air dry and was ground to a fine powder using a mortar and pestle.Cements were prepared by independently mixing the treated glasses at a1.4:1 P:L ratio with a cement-forming copolymer solution made by mixingthe ingredients set out below in Table IX.

                  TABLE IX                                                        ______________________________________                                        Ingredients                 Parts                                             ______________________________________                                        Dry copolymer of PREPARATORY EXAMPLE 2                                                                    40                                                Water                       36                                                2-Hydroxyethyl methacrylate 24                                                CPQ                         0.5                                               BHT                         0.05                                              ______________________________________                                    

As a comparison, a cement composition ("Control E") was made by mixingat the same P:L ratio untreated VITREBOND glass powder and thecement-forming liquid of Table IX. Set out below in Table X are the runno., the weight % A-1100 silane and the CS and DTS for the finalcements.

                  TABLE X                                                         ______________________________________                                        Run No.   Wt. % Silane CS, MPa  DTS, MPa                                      ______________________________________                                        1         0.1          89       19                                            2         0.5          80       10                                            3         1.0          63        6                                            4         5.0          72       13                                            Control E 0            63       12                                            ______________________________________                                    

The data in Table X illustrate the significant improvement in physicalproperties provided by addition of a small amount of silanol to theglass (Run no. 1). As greater amounts of silanol were added to the glass(Run nos. 2-4), working time greatly decreased making it very difficultto obtain accurate physical property determinations.

EXAMPLE 25

Treated Fluoroaluminosilicate Glass

To 2.0 pans A-174 silane was added 12.6 parts methanol, 12.6 parts waterand 0.22 parts acetic acid. The ingredients were mixed together andstirred magnetically for 30 minutes at ambient temperature. The mixturewas added to 50 parts of a glass powder like that of PREPARATORY EXAMPLE8 and slurried for 1.5 hours at ambient temperature. The slurry was thenpoured into a plastic-lined tray and dried for 20 hours at 45° C. Thedried powder was sieved through a 74 micron mesh screen.

EXAMPLES 26-42

The glasses of PREPARATORY EXAMPLE 8 and EXAMPLE 25 and the filler ofPREPARATORY EXAMPLE 9 were treated with one or more additional organiccompounds as listed in Table XI. The treatments were applied by mixingneat solutions (i.e., without the aid of a volatile solvent) of theadditional organic compound or compounds with the glass or filler untilthe glass or filler was uniformly coated. With the exception of Examples41 and 42 the treated glass or filler was essentially a dry powder afterthe treatment solution was applied. In contrast, Examples 41 and 42 werecoated with sufficient additional organic compound such that theresultant mixture was no longer a powder but rather a viscous paste.

Cement test samples were prepared by combining the treated glasses andfillers with a cement-forming copolymer solution (Liquid B of Table IV).The relative weight ratio of additional organic compound, glass, fillerand liquid is listed in Table XI for each example. Also set out below inTable XI are the example number, the type of additional coating orcoatings and the value of the CS, DTS and fracture toughness ("K_(1c) ")of each example. The experimental values for CS, DTS and K_(1c)represent the mean value of at least 5 experimental runs

The fracture toughness of the cement test samples was measured using theshort rod specimen geometry. This test is presently believed to measurethe resistance of a dental restorative material (e.g., a dental cementor composite) to crack propagation. The samples of this invention weretested in the manner described by L. M. Barker in a research articleentitled: "Compliance Calibration of a Family of Short Rod and Short BarFracture Toughness Specimens," Engineering Fracture Mechanics Vol. 17,No. 4, pp. 289-312, 1983.

The test sample geometry of the short rod specimen is illustrated inFIG. 1(a) on page 291 of the Barker article. The specimens of thepresent invention follow this geometry with the following deviations.The test samples were molded into 4 mm diameter cylinders of 8 mm lengthand then notched as illustrated in FIG. 1(a) using diamond cutting saws.Therefore, referring to the table accompanying FIG. 1(a): "B" is 4 mm,"L" is 8 mm, "1_(o) " is 4 mm and "τ" is 150 microns for the specimensof this invention. In addition the loadline is 2 mm from the edge of thesample and the chevron angle "θ" is 56°.

The fracture toughness of the cements were calculated using thefollowing equation:

    K.sub.1c =f(1/B)(F/B.sup.1.5)                              (equation 3 from Barker)

where "F" is the failure load, "B" is the specimen diameter and "f(1/B)"represents the stress intensity factor coefficient. The stress intensityfactor coefficient is calculated using equation (6) of the Barkerreference and was experimentally determined to be 24.83 for thespecimens of this invention.

                                      TABLE XI                                    __________________________________________________________________________                            Additional                                               Table IV   Prep Ex.                                                                           Prep Ex.                                                                           Organic                                                  Liq. B                                                                             Example 25                                                                          8    9    Compound(s)                                                                              CS,                                                                              DTS,                                                                              K.sub.1C,                           Ex.                                                                              Parts                                                                              Parts Parts                                                                              Parts                                                                              (Parts)    MPa                                                                              MPa MN/m.sup.1.5                        __________________________________________________________________________    F  12.5 --    75   --   --          63                                                                              12  0.87                                G  12.5 --    --   75   (12.5) PEG.sub.200 DMA                                                                   210                                                                              15  0.49                                H  12.5 75    --   --   (12.5) TEG  54                                                                               9  --                                  26 12.5 71    --   --   --         214                                                                              16  0.81                                27 12.5 --    75   --   (12.5) PEG.sub.200 DMA                                                                   155                                                                              20  0.90                                28 12.5 75    --   --   (12.5) PEG.sub.200 DMA                                                                   222                                                                              32  1.00                                29 12.5 52.5  --   22.5 (12.5) PEG.sub.200 DMA                                                                   215                                                                              26  --                                  30 12.5 37.5  --   37.5 (12.5) PEG.sub.200 DMA                                                                   253                                                                              38  0.86                                31 12.5 75    --   --   (12.5) PEG.sub.400 DMA                                                                   112                                                                              14  0.65                                32 12.5 75    --   --   (12.5) PEG.sub.600 DMA                                                                   141                                                                              16  0.57                                33 12.5 75    --   --   (12.5) TEGDMA                                                                            223                                                                              34  --                                  34 9.0  75    --   --   (16.0) TEGDMA/PC.sup.1                                                                   249                                                                              29  0.97                                35 12.5 75    --   --   (6.25) PEG.sub.200 DMA                                                                   262                                                                              31  1.08                                                        (6.25) BIS-GMA                                        36 12.5 75    --   --   (6.25) PEG.sub.200 DMA                                                                   249                                                                              28  --                                                          (6.25) BIS-GMA                                        37 12.5 75    --   --   (8.75) PEG.sub.200 DMA                                                                   230                                                                              21                                                              (3.75) TAGU                                           38 12.5 37.5  --   3.75 (6.25) PEG.sub.200 DMA                                                                   276                                                                              38  1.16                                                        (6.25) BIS-GMA                                        39 12.5 75.0  --   --   (12.5) SR350                                                                             221                                                                              33  0.50                                40 8.0  36.0  --   36.0 (8) PEG.sub.200 DMA                                                                      293                                                                              49  1.23                                                        (10) BIS-GMA                                                                  (2) Glyceroldimeth-                                                           acrylate                                              41 8.0  48.0  --   24.0 (8) PEG.sub.200 DMA                                                                      273                                                                              47  1.21                                                        (10) BIS-GMA                                                                  (2) Glyceroldimeth-                                                           acrylate                                              42 8.0  72.0  --   --   (10) PEG.sub.200 DMA                                                                     241                                                                              39  1.10                                                        (10) BIS-GMA                                          __________________________________________________________________________     .sup.1 Triethylene glycol dimethacrylate saturated with "Calibre 300"         grade polycarbonate, available from Dow Chemical Co.                     

The data shown above illustrate the significant increases in CS, DTS andK_(1c) provided by the treatments of the present invention. For example,control EXAMPLE F (using untreated fluoraluminosilcate glass and noadditional organic coating) and EXAMPLE 26 (using silanol treatedfluoroaluminosilcate glass and no additional organic compound treatment)had CS values of 63 and 214 MPa respectively. Cements of the presentinvention which had both a silanol coating and an additional organiccompound treatment, e.g., EXAMPLE 40, had CS values of up to 293 MPa.The K_(1c) value of the untreated control, EXAMPLE F, was 0.87 MN/m¹.5,while in many cases cements of the present invention which had both asilanol coating and an additional organic compound treatment had K_(1c)values up to 1.4 times higher (1.23 MN/m¹.5). Likewise the DTS of thecements of the present invention are two to four times the value of theuntreated control.

EXAMPLE 27 illustrates the improvement which can be obtained usingglasses that contain the additional organic compound treatment but donot contain the silanol treatment of the present invention. A directcomparison of EXAMPLE 27 and control EXAMPLE F illustrates theadvantages of the additional organic coating when no silanol treatmentis applied (CS is increased from 63 MPa to 155 MPa; while the DTS andK_(1c) values show a more modest increase).

Control EXAMPLE G illustrates the utility of further treating silanoltreated non reactive filler particles with an additional organiccompound. While the CS and DTS values of this control are quiterespectable (210 and 15 MPa respectively), the fracture toughness valueis relatively low (0.49 MN/m¹.5). This is believed to be due to theinability of the non-reactive filler to participate in the cementreaction with Liquid B. When this same filler is mixed with a reactiveglass (e.g., the glass of either PREPARATORY EXAMPLE 8 or EXAMPLE 25)the CS, DTS and fracture toughness improve. EXAMPLES 29, 30, 38, 40 and41 exemplify this combination.

Control EXAMPLE H illustrates the effect of coating a silanol treatedfluoroaluminosilcate glass with a triethyleneglycol ("TEG") compound.This compound differs from the solutions of the present invention inthat it is incapable of further polymerization (i.e., TEG is incapableof participating in either the cement reaction or a hardening reactionwith the other monomers or polymers of the cement composition). ControlEXAMPLE H has a lower CS and DTS values than a cement using an untreatedglass.

Although this invention has been described using certain illustrativeexamples, it should be understood that the invention is not limited tothe specific exemplary embodiments shown in this specification.

We claim:
 1. A method for treating fluoroaluminosilicate glass,comprising the steps of:a. mixing finely-divided fluoroaluminosilicateglass with an aqueous silanol solution, and b. drying the glass, saidglass being capable of forming a cement when mixed with water and apolyalkenoic acid.
 2. A method according to claim 1, wherein the silanolis ionic and at least 0.1 percent hydrolyzed.
 3. A method according toclaim 1, wherein the silanol is nonionic and at least 0.1 percenthydrolyzed.
 4. A method according to claim 1, wherein the solution isacidic and the silanol is ethylenically-unsaturated.
 5. A methodaccording to claim 1, wherein the solution is basic and the silanol isethylenically-unsaturated.
 6. A method according to claim 1, wherein thesolution is acidic and the acid is borne on the silanol.
 7. A methodaccording to claim 1, wherein the solution is acidic and the acid isborne on the silane from which the silanol is formed.
 8. A methodaccording to claim 1, wherein the solution is basic and the base isborne on the silanol.
 9. A method according to claim 1, wherein thesolution is basic and the base is borne on the silane from which thesilanol is formed.
 10. A method according to claim 1, wherein thesilanol has one or more pendant carboxylic acid groups.
 11. A methodaccording to claim 1, wherein the silanol has the formula R_(n)Si(OH)_(4-n) wherein R is a non-hydrolyzable polymerizable organic groupand n is one to three.
 12. A method according to claim 1, wherein thesilanol was formed by hydrolysis of the alkoxy groups of anethylenically-unsaturated alkoxysilane of the formula: ##STR3## whereinR¹, R², R³ and R⁴ are independently H, CH₃, COOH or CH₂ COOH; R⁵ and R⁶are independently divalent alkylene linking groups; each R⁷ isindependently an alkyl group; T¹ and T² are independently terminatinggroups such as H or alkyl; w is 0 to 12; and each of x, y and z is atleast one.
 13. A method according to claim 1, wherein the solution isacidic and the acid is present as a separate component of the solution.14. A method according to claim 1, wherein the solution is basic and thebase is present as a separate component of the solution.
 15. A methodaccording to claim 13, wherein the acid is selected from the groupconsisting of formic acid, acetic acid, trifluoroacetic acid, propionicacid, pentafluoropropionic acid, hydrochloric acid, nitric acid,sulfuric acid, phosphoric acid, lactic acid, citric acid and tartaricacid, and said solution further comprises a solvent selected from thegroup consisting of methanol, ethanol, propanol, isopropanol,tert-butanol and acetone.
 16. A method according to claim 14, whereinthe base is selected from the group consisting of sodium hydroxide,ammonium hydroxide, potassium hydroxide, barium hydroxide, lithiumhydroxide, magnesium hydroxide, calcium hydroxide, sodium bicarbonate,ammonia, methylamine, dimethylamine, trimethylamine, ethylamine,diethylamine, n-propylamine, n-butylamine, isobutylamine,sec-butylamine, and tert-butylamine and said solution further comprisesa solvent selected from the group consisting of methanol, ethanol,propanol, isopropanol, tert-butanol and acetone.
 17. A method accordingto claim 1, wherein the solution contains about 0.1 to about 20 weight %silanol and about 80 to about 99.9 weight % water.
 18. A methodaccording to claim 1 wherein the glass is further treated with anadditional organic compound.
 19. A method according to claim 18, whereinthe additional organic compound has at least one functional groupselected from the group consisting of acrylates and methacrylates.
 20. Amethod according to claim 18, wherein the additional organic compoundhas a weight avenge molecular weight per double bond of between about100 and
 5000. 21. A method according to claim 18, wherein the additionalorganic compound comprises polyethyleneglycol dimethacrylate.
 22. Amethod according to claim 18, wherein the silanol solution and theadditional organic compound are sequentially applied to the glass.
 23. Amethod according to claim 1, wherein the solution contains about 0.1 toabout 20 weight % silanol, at least about 40 weight % volatile solvent,and about 20% to about 60 weight % water.
 24. A method according toclaim 1, wherein the solution contains about 0.1 to about 10 weight %silanol, water, and sufficient acid to provide a pH of about 1 to about4.5.
 25. A method according to claim 1, wherein the solution containsabout 0.1 to about 10 weight % silanol, water, and sufficient base toprovide a pH of about 8 to about
 12. 26. A method according to claim 1,wherein the dried treated glass a forms a cement upon being mixed withwater and a polyacrylic acid, and one day after forming said cementreleases fluoride at a rate greater than a like glass having a silanetreatment.
 27. A method of making a glass ionomer cement, comprising thesteps of:a. treating finely-divided fluoroaluminosilicate glass with anaqueous silanol solution; b. mixing the treated glass with apolyalkenoic acid; and c. allowing the mixture of step b) to harden. 28.A method according to claim 27, wherein the solution is acidic and thesilanol is ethylenically-unsaturated.
 29. A method according to claim27, wherein the silanol has the formula R_(n) Si(OH)_(4-n) wherein R isa non-hydrolyzable polymerizable organic group and n is one to three.30. A method according to claim 27, wherein the silanol was formed byhydrolysis of the alkoxy groups of an ethylenically-unsaturatedalkoxysilane of the formula: ##STR4## wherein R¹, R², R³ and R⁴ areindependently H CH₃, COOH or CH₂ COOH; R⁵ and R⁶ are independentlydivalent alkylene linking groups; each R⁷ is independently an alkylgroup; T¹ and T² are independently terminating groups such as H oralkyl; w is 0 to 12; and each of x, y and z is at least one.
 31. Amethod according to claim 27, wherein the solution is acidic and theacid is present as a separate component of the solution.
 32. A methodaccording to claim 27, wherein the glass is further treated with anadditional organic compound.
 33. A method according to claim 32, whereinthe additional organic compound has at least one functional groupselected from the group consisting of acrylates and methacrylates.
 34. Amethod according to claim 32, wherein the silanol solution and theadditional organic compound are sequentially applied to the glass.
 35. Amethod according to claim 27, wherein the solution contains about 0.1 toabout 20 weight % silanol, at least about 40 weight % volatile solventand about 20 to about 60 weight % water.
 36. A method according to claim27, wherein one day after mixing with the polyalkenoic acid the cementreleases fluoride at a rate greater than a like glass having a silanetreatment.
 37. A method according to claim 27, wherein twelve days aftermixing with the polyalkenoic acid the cumulative fluoride release rateof the cement is at least 52 μg/g.